21 research outputs found
Spectrum of the Y=2 Pentaquarks
By assuming a mass formula for the spectrum of the Y=2 pentaquarks, where the
chromo-magnetic interaction plays a main role, and identifying the lightest
state with the Theta^+(1540), we predict a spectrum in good agreement with the
few I=0 and I=1 candidates proposed in the past.Comment: 12 pages, 4 figures, LaTe
Chiral doublers of heavy-light baryons
We discuss the consequences of the chiral doubling scenario for baryons built
of heavy and light quarks. In particular, we use the soliton description for
baryons, demonstrating why each heavy-light baryon should be accompanied by the
opposite parity partner. Our argumentation holds both for ordinary baryons and
for exotic heavy pentaquarks which are required by the symmetries of QCD to
appear in parity doublets, seperated by the mass shift of the chiral origin.
Interpreting the recently observed by BaBaR, CLEO and Belle charmed mesons with
assignment as the chiral partners of known and mesons,
allows us to estimate the parameters of the mesonic effective lagrangian, and
in consequence, estimate the masses of ground states and excited states of both
parities. In particular, we interpret the state recently reported by the H1
experiment at HERA as a chiral partner of yet
undiscovered ground state pentaquark .Comment: 10 pages, in v2 some typos corrected, references adde
A Naturally Narrow Positive Parity Theta^+
We present a consistent color-flavor-spin-orbital wave function for a
positive parity Theta^+ that naturally explains the observed narrowness of the
state. The wave function is totally symmetric in its flavor-spin part and
totally antisymmetric in its color-orbital part. If flavor-spin interactions
dominate, this wave function renders the positive parity Theta^+ lighter than
its negative parity counterpart. We consider decays of the Theta^+ and compute
the overlap of this state with the kinematically allowed final states. Our
results are numerically small. We note that dynamical correlations between
quarks are not necessary to obtain narrow pentaquark widths.Comment: 10 pages, 1 figure, Revtex4, two-column format, version to be
published in Phys. Rev. D, includes numerical estimates of decay width
Light-Front Approach for Heavy Pentaquark Transitions
Assuming the two diquark structure for the pentaquark state as advocated in
the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and
parity-odd triplet heavy pentaquark baryons. The theoretical estimate of
charmed and bottom pentaquark masses is quite controversial and it is not clear
whether the ground-state heavy pentaquark lies above or below the strong-decay
threshold. We study the weak transitions of heavy pentaquark states using the
light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark
transition form factors can be expressed in terms of three Isgur-Wise
functions: two of them are found to be normalized to unity at zero recoil,
while the third one is equal to 1/2 at the maximum momentum transfer, in
accordance with the prediction of the large-Nc approach or the quark model.
Therefore, the light-front model calculations are consistent with the
requirement of heavy quark symmetry. Numerical results for form factors and
Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to
Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to
Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q,
Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light
octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and
Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+
pi- are estimated to be at the level of 10^{-3} and a few percents,
respectively.Comment: 33 pages, 3 figures, version to be published in Phys. Rev.
Structure and Mechanical Properties of TiAlSiY Vacuum-Arc Coatings Deposited in Nitrogen Atmosphere
The effect of a negative bias potential applied to the substrate on elemental composition, structure,
and mechanical properties of vacuum-arc TiAlSiY nitride coatings is investigated by different methods. It is
ascertained that applying a high (up to –500 V) bias voltage leads to a selective sputtering of target as well as
significant microdeformation of the coating, small-sized growth of crystallites, and their preferred orientation
along the [110] direction. In this case, the coating deposited has a low hardness H = 6.95 GPa and propensity
to intense wear under scratch and tribological tests. Crystallites with stoichiometric composition ~140 nm in
size and [111] preferred orientation perpendicular to the surface of growth are formed at the bias potential
about –200 V, and superhard (H = 49.5 GPa) and wear-resistant coatings are grown under such conditions.
The mechanisms of formation of the structure of multielement coatings are discussed. It is shown that for-
mation of an amorphous phase and nanocrystal [110] texture takes place at a high bias potential owing to the
process of radiation-stimulated selective spraying of the target. Formation of microstrained crystallites 10 nm
in size caused by the weakening of interatomic bonds is observed in the coating under such deposition condi-
tions, and it leads to the decrease in coating hardness and fast destruction during tribological testing. Sub-
stantial bias voltage dependence of deposited coating properties is established in our investigations
Search for a strongly decaying neutral charmed pentaquark
We present a search for a charmed pentaquark decaying strongly to
. Finding no evidence for such a state, we set limits on the cross
section times branching ratio relative to and under particular
assumptions about the production mechanism.Comment: To be published in Physics Letters
Structural features of iron vacuum condensates alloyed with tungsten
Initial structure and composition of Fe-W vacuum deposited films were studied using the methods of transmission electron microscopy, X-ray diffraction, energy-dispersive spectroscopy, and X-ray fluorescence analysis. It was shown that tungsten microalloying resulted in the grain dispersion of iron matrix. The tungsten non-homogeneous distribution within each grain has been revealed. The features observed are explained by the alloying component grain-boundary segregations formed under condensation of two-component vapor
Structure and strength characteristics of dispersion-hardened composite foils (films) based on iron and nickel
Effects of hardening components (W, SiO, Al₂O₃, and ZrO₂) on structure and physical-mechanical characteristics of Fe and Ni composites were studied. The content of the hardening phases was up to 2 vol.%. It was shown experimentally that physical-mechanical characteristics of the prepared nano- crystalline materials were defined by the structure and inhomogeneous distribution of the hardening phase within a grain. The reasons for high thermal stability of the nano-composites were established. The factors determining the nano-composite relaxation resistibility and resources for its increasing were revealed